Compositions have been developed for protecting marine surfaces from fouling organisms, including a linear or cross-linked polymer having a siloxane backbone and trisubstituted tin radicals such as tributyl tin bonded to silicon atoms by way of an oxygen atom. The biologically active polymer can be used for forming coatings for steel, concrete, or other surfaces exposed to marine environments for inhibiting the growth of fouling organisms. In some embodiments the polymer is present as an additive in a coating composition. In other embodiments the cross-linked polymer forms a portion of the binder of the coating.
U.S. Pat. No. 4,080,190 by Law and Gysegem, which is hereby incorporated by reference, discloses such compositions with a variety of organotin radicals and synthesis techniques. The ratio of tin to silicon atoms in the polymer can be varied for obtaining different properties in the polymer. When the proportion of tin is low, a cross-linked polymer can be formed by hydrolysis and polycondensation of a siloxane-tin precursor. In an exemplary embodiment the precursor is formed by reaction of tetraethoxysilane or a short chain ethosyxiloxane with a carboxylic acid derivative containing a tin radical, such as tributyltin acetate. A prepolymer can be formed by partially or completely hydrolyzing the precursor. Water and a hydrolysis catalyst such as hydrogen ion or hydroxyl ion are added to the solvent. Upon evaporation of the solvent polycondensation occurs, yielding the desired polymer.
It is sometimes convenient to hydrolyze the precursor to a prepolymer before completing a coating composition since prehydrolysis can reduce the curing time of a coating. Polycondensation of the prepolymer has heretofore been inhibited by retaining the prepolymer in ethyl alcohol or similar solvent. Ethyl alcohol is a product of hydrolysis of the precursor when, for example, an ethoxysilicate is employed in the synthesis. When such a coating is applied, evaporation of ethyl alcohol results in polycondensation in the coating.
Ethyl alcohol and similar water miscible solvents may not be compatible with other ingredients in the coating composition. This is particularly true when the coating composition includes a chlorinated rubber, for example. It is therefore desirable to provide a solution containing polymeric material which is compatible with such coating compositions.